1. Field of Invention
This invention relates to a device for detecting the occurrence of misfires in an internal combustion engine, and more particularly to a misfire detector for an internal combustion engine which utilizes variations in rotation of the engine to detect the occurrence of a misfire in it with high accuracy.
2. Description of Prior Art
There are available a variety of misfire detecting devices in the art. A misfire detecting system utilizing variations in rotation of the engine has been proposed, for instance, by Unexamined Japanese Patent Publication (Kokai) Sho-58-19532/(1983). The conventional device is designed as follows: In the device, there are provided rotation detecting intervals in the first half and the second half of the stroke of expansion of the engine, respectively, and when the difference in the speeds of rotation detected in those intervals is larger than a predetermined value, it is determined that a misfire has occurred in the engine.
In another conventional misfire detecting device, a deviation in the period of rotation is detected every ignition cycle, and it is divided by the average value of the periods of rotation to obtain a rotation variation rate, from which it is determined whether or not a misfire has occurred.
As is apparent from the above description, the conventional method is based on the variations in rotation of the engine; more specifically, the detection of a misfire is based on the fact that when a misfire occurs with a cylinder of the engine, the period of rotation of the cylinder is increased. However, the conventional device suffers from the following difficulty: In the cases where, in a multicylinder engine, a misfire occurs with a certain cylinder continuously, and it occurs with it intermittently, the variations in rotation are different in pattern, and therefore it is impossible for the device to detect the occurrence of a misfire with high accuracy (in order to meet the U.S. regulation OBD-II, the detection must be made to a misfire percentage of about 2%).